The present disclosure relates to optical thin films and, more particularly, to systems and methods of using tunable lasers in the design, manufacture and implementation of optical thin films.
Optical computing devices, also commonly referred to as “opticoanalytical devices,” can be used to analyze and monitor a substance in real time. Such optical computing devices will often employ a light source emitting electromagnetic radiation that reflects or refracts from a substance and optically interacts with an optical processing element to determine quantitative and/or qualitative values of one or more physical or chemical properties of the substance. The optical element may be, for example, an integrated computational element (ICE), also known as a multivariate optical element (MOE), which may act as an optical interference filter that can be designed to operate over a continuum of wavelengths in the electromagnetic spectrum from the UV to mid-infrared (MIR) ranges, or any sub-set of that region. Electromagnetic radiation that optically interacts with the substance is changed and processed by the ICE so as to be readable by a detector, such that an output of the detector can be correlated to the physical or chemical property of the substance being analyzed.
An exemplary ICE (hereafter “ICE core”) typically includes a plurality of optical layers consisting of various materials whose index of refraction and size (e.g., thickness) may vary between each layer. The design of an ICE core (referred to herein as an “ICE design”) refers to the number and thicknesses of the respective layers of the ICE core. The layers may be strategically deposited and sized so as to selectively pass predetermined fractions of electromagnetic radiation at different wavelengths configured to substantially mimic a regression vector corresponding to a particular physical or chemical property of interest of a substance. Accordingly, an ICE design will exhibit a transmission function that is weighted with respect to wavelength. As a result, the output light from the ICE core conveyed to the detector may be related to the physical or chemical property of interest for the substance.
Ellipsometry is an optical measurement technique that may be used in the design and fabrication of optical processing elements, such as ICE cores or other optical thin films. For example, during fabrication, ellipsometry may be used to monitor the progress of the deposition process to ensure that parameters of the optical thin films are within specification of the thin-film design. Similar to the workings of an optical computing device, ellipsometry uses a light source that emits electromagnetic radiation to optically interact with a layer of the optical processing elements deposited on a substrate, thereby generating reflected electromagnetic radiation that may be used to measure or characterize the layer. Example characterization information that may be measured may include, but is not limited to, surface roughness, layer thickness, and refractive index of the thin film layer or design. The light source used in the ellipsometry measurement system greatly affects what information is determinable and the accuracy thereof. Typical light sources used in ellipsometry measurement systems include broadband light sources, such as a Tungsten-filament lamp or a light bulb.